The present invention relates to an apparatus for continuous purification of liquids, and in particular to an apparatus for the continuous clarifying of liquids with suspended solid substances by means of the dissolved gas flotation process.
As is known, in the dissolved gas flotation process, also known as differentiated pressure flotation, the flow of liquid to be treated entering into the flotation container, or part of said flow, is preliminarily saturated with gas which is dissolved in the liquid, under pressure, in a special pressurization tank. A sharp pressure reduction is then performed by means of a reduction valve immediately before the entry of the liquid into the flotation cell, so that all the supersaturated gas is released in the form of microscopic bubbles (30-100 .mu.) which are finely dispersed in the entire volume of liquid and adhere to the solid particles suspended in the liquid, forming an aggregate with a relative density which is lower than that of the liquid from which it separates, moving toward the surface. The solid particles concentrated at the surface are then removed by means of a spillway system.
In conventional apparatus, the hydraulic load in the tank is normally comprised between 3 and 5 m.sup.3 /h.times.m.sup.2 of tank surface, with minimum permanence times of approximately 30 minutes; these conditions occur in flotation tanks with a liquid or hydraulic head generally comprised between 2 and 3 m.
The U.S. Pat. No. 4,022,696 describes a flotation cell capable of operating with high hydraulic loads (up to 10 m.sup.3 /h.times.m.sup.2) which allows to reduce tank permanence times considerably, in practice reducing the depth or liquid head of said tank.
This apparatus, however, has considerable constructive complexity, since a structurally considerably complicated and expensive movable system for the distribution of the liquid to be clarified and for drawing the clarified liquid is provided.
This system furthermore entails the use of tubes and partitions, both for distributing the liquid to be treated and for drawing the clarified liquid, which can easily be dirtied and are difficult to clean rapidly and efficiently.